Television system



March 28, 1939.

R. C. BALLARD TELEVI S ION SYSTEM Filed July 19, 1932 2 Sheds-Sheet l MFigi z2 z o f f o y L RADIO TRANSMITTER `I"IODIJL6CI'0R AMPLIFIERAMPLlFu-:R -18 14 wsrfaum" y u la 28 Il AMPLIFIER Lo eRandcxlLC.BoLU.cLr*d,

Hl ATTORNE Y March 28, 1939. R. c. BALLARD A'IELEVISION SYSTEM FiledJuly 19, 1952 2 Sheets-Sheet 2 mvENw-on Randall C. Ballard.,

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HIS ATTORNEY Patented Mar. 28, 1939 PATENTI oFFlcE TELEVISION SYSTEMRandall C. Ballard, Marion, Ind., assignor to Radio Corporation ofAmerica, a corporation of Delaware Application July 19, 1932, Serial No.623,325 14 Claims. (01.' P18-'1.6)

My invention relates to improvements in television systems and, moreparticularly, to an improved method of scanning.

In the art of television, wherein a moving pic- 5 ture film with a soundtrack thereon is the object televised, satisfactory results have beenobtained by using a scanning disc at the transmitting station fortransmitting the picture and a cathode ray tube at the receiving stationfor re;

l producing the picture. An important advantage of the cathode ray tubefor receiving purposes resides in the feature of retentivity offluorescence of the fluorescent screen with which the tube is provided,which screen is scanned by the cathl ode ray. In this connection, i-thas been determined that, for the purpose of making use of thisfluorescence to the best advantage, the received picture frequencyshould not be materially greater than sixteen pictures per second.However, when using standard sound-film, it is necessary, at thetransmitter, to run the film at the usual normal rate of 24 frames asecond to reproduce the sound faithfully.

Various methods and constructions have been gr, proposed for the purposeof permitting simultaneous occurrence of the two conditions of operationreferred to, that is, scanning the film at a rate not greater thansixteen pictures per second, and running the film at the usual rate of24 frames per second.

One of these methods proposed heretofore has been to run the film at thenormal rate of 24 frames a second, but to scan only every second, third,or fourth picture of the lm. Another method proposed has been to make aslow-speed film from the standard film, in which case the correctreproduction of the sound was obtained with the film running at a speednot greater than sixteen pictures per second, and every picture wasscanned. These methods, as well as the various other methods proposedheretofore, are costly and/or cumbersome.

With the foregoing in mind, it is one of the objects of my invention toprovide an improved television system, for the transmission of standardsound-film, wherein the film is run at the normal rate and is scanned insuch a manner as to obtain full advantage of the fluorescent effect in acathode ray tube at the receiving station.

Another object of my invention is to provide an improved televisionsystem for the transmission of sound film, wherein the frequency channelrequired for television is reduced without changing from the standardrate of 24 pictures a second at which the nlm is run.

Another object of my invention is to provide an improved method ofoperation whereby the number of picture lines can be substantially in- 5creased without necessitating an increase in the required frequencychannel.

Another object of myinvention is to provide an improved method wherebythe optical effect, referred to as icker, is eliminated or reduced 10 toa. negligible degree.

Other objects and advantages will hereinafter appear.

For the purpose of illustrating my invention, an embodiment thereof isshown in the drawings, l5 wherein- Figure 1 is a diagrammatic view of atelevision transmitting system constructed and operable in accordancewith my invention;

Fig. 2 -is an enlarged elevational view of the 20 scanning disc in Fig.1, looking toward the left in this figure; l

Fig. 3 is a diagrammatic view of a television receiving systemconstructed and operable in accordance with my invention; and 25 Fig. 4is a schematic illustration of the manner in which the cathode ray scansthe uorescent screen in Fig. 3.

My invention resides in the improved system and method of operation ofthe character here- 30 inafter described and claimed.

The transmitting system shown in Fig. 1 comprises a scanning disc IIIprovided with apertures at its edge arranged on a circle concentric,with the axis of rotation of the disc. Light from a 35 suitable sourceI2 passes through these apertures and through a standard sound film I4onto a photoelectric cell I6. Picture signals are thereby developed and,after passing through a plurality of amplifiers I8 and. 20 and amodulator 40 22, may be radiated by a suitable radio transmitter 24 orotherwise conveyed to distant receiver-locations.

The film I4 is supported in the usual manner, and is fed along at thenormal rate of 24 pic- 45 tures a second.

For the purpose of developing and transmitting synchronizing and framingimpulses, the disc III is provided with other apertures through which50,

light from a source 26 passes to a photoelectric cell 28. These impulsesare amplified by an amplier SI), and then pass to the amplier 20 by wayof av connection 32. In this manner, the synchronizing and framingimpulses are trans- 55 end, with a fluorescent screen 52 mitted in thesame radio channel with the picture signals.

Coming now to a more detailed explanation of the construction and mannerof operation oi' the disc I 6. reference is made to Fig. 2.

Assuming that it is desired to reproduce an 8 0 line picture at thereceiving station, the disc I0, for this purpose, is provided with 81apertures A1 to Asi, and is rotated at the rate of twelve revolutions asecond, or x/2 the picture frequency at which the nlm I4 is run. Theoperation, therefore, is such that each picture of the lm Ais scannedalong 40.5,lines.

The disc is also provided with .a'plurality of apertures a1 to an. equalin number to the picture apertures, these apertures being so arranged,as will be well understood, that a4 synchronizing impulse is developed?and ,t ransrnitted at the end of each picture line. One: of` theseapertures, that is, the aperture a for example, is made substantiallylarger than the others for the purpose of developing a framing impulse.I is provided with another framing aperture or opening, disposed asshown, diametrically opposite the openingzgg, and between synchronizingapertures ani-sind The reason for this particular arrangement "will beunderstood during the course of the following description andexplanation; 3

The disc III is rotated at the rate oi' one revolution for everytwofr'ames of the film. As the disc is provided with an Aodg!` number ofpictur apertures, that is, 81, eachpicture of the lm will be scannedalong 40.5 lines.` At the end of the scanning fperiod for the ilrst 40.5lines, the framing opening 34 wilf be in position between the lightsource 26 andfthe photoelectric cell 26 to effect transmission of aframing impulse. At the end of the next scanning period, during whichthe next picture of the illm is scanned along 40.5 lines, the apertureaas will be in poqtion to effect transmission of a second framingimpulse. This second framing impulse'oocurs at the end of the 81stscanning line, at the end of each complete revolution of the disc.

In the receiving system, as shown in Fig. 3, the transmitted picturesignals and the synchronizing and framing impulses are received by asuitable radio receiver 36, and appear across resistances 38, 46 and 42.'Ihe picture signals, which are positive in sign, are taken from theresistance 36 and are applied, by a connection 44, to the control grid46 of a cathode ray tube 46. In this manner, the intensity of the ray 60is varied in accordance with the picture signals.

'I'he synchronizing and framing impulses ldo not interfere withreproduction of the picture -for the reason that they are negative insign and, furthermore. occur at the ends of the scanning lines andbetween frames, respectively.

'I'he cathode ray tube is provided, at its large which the ray 50 iscaused to scan in a manner simulating the scanning action at thetransmitter. For this purpose, the ray is deflected horizontally 972times a second by causing a saw-tooth current wave, at this frequency,to pass througha plurality of horizontal deflection lcoils 54. Thesecoils are supplied from a suitable generator 56 for this purpose, whichis locked in step with the line-scanning frequency at the the resistance40 and applied to the input circuit of this generator. The frequency of972 cycles is required on account of the fact that the transmitter by`the received synchronizingimpulses taken from transmitting disc has 81picture apertures and rotates at the rate of twelve revolutions asecond.

The ray 60 is deflected vertically at the rate of 24 times a second byelectromagnetic coils 56 through which a saw-tooth current wave at thisfrequency is caused to pass. A suitable generator 60 operates togenerate this wave. and is locked in step with the framing frequency atthe trans'- mitter by taking the framing impulses from the Yof mypresent invention, they are not illustrated in detail.

The scanning action at the receiving station will now be explained, withreference to Fig. 4, which is a schematic representation of theapproximate path along which the ray scans the fluorescent screen 62,the figure being considered as a view looking toward the left in Fig. 3.

The area of the fluorescent screen which is scanned by the ray 66 isalways the same, that is, the area ABCD.

'I'he ray 66 is deflected to the right, for scanning line I, during thetime that the picture aperture A1 is effective at the transmitter.Similarly, the raw is deflected to the right again, for

scanning line 2, during the time that the pictureA aperture Az at thetransmitter is effective, and so on. For the line 39, however, the rayis only deflected half way to the point E, at which instant the screenwill have been scanned along 38.5 lines. 'Ihis action is caused by thefact that, at this instant at the transmitter, the aperture 34 comesinto position to effect transmission of a framing impulse, whereupon thevertical deflecting coils l cause the ray to return upwardly. 'Iheperiod for upward return is not instantaneous, but requires alength oftime corresponding to several scanning-line periods: 'I'he ray,therefore, reaches the point F as the picture aperture A3. completes itsscanning action at the transmitter for the line 39. 'I'he next scanningline 40 at the receiver takes place during the period of operation ofthe picture aperture A40 at the transmitter. At the completion of thescanning action at the receiver for 40.5 lines, that is, at the point G,the ray is started downward again, as before. 'Ihe next scanning of thescreen 62, therefore, begins from the point G rather than from the pointA, the lines of this second scanning being represented in the figure bydash lines. 0n account of this action, the line 40.5-41 and the lines 42to 79, all comprising the second scanning, are interwoven with respectto, or occur between the lines 1 to 38.5 of the ilrst scanning. At thecompletion of the line 79, the aperture aan at the transmitter is inposition to eifect transmission of a second framing impulse, whereuponthe rayl is returned vertically to the point B along the path shown. Theray reaches the point H at the instant kof completion of what would havebeen the scanning line 80, and reaches the point B at the completion ofwhat would have been theline 81. In the present explanation, it has beenassumed that return deflection of the ray horizontally occurs in zerotime. From .the

point B, therefore, the ray returns to the point A, and the cycle,corresponding to one complete revolution of the transmitting disc l0, iscompleted.

From the foregoing it will be seen that the screen 52 is scannedhorizontally along '77 effectivelines, and that a time periodcorresponding to 4 lines is used in the vertical return of theA ray. Theresult is that, to the eye, the cathode ray tube presents what appearsto be a normal 'VI-line picture. Actually, however, the tube ispresenting .a series of 38.5 line pictures which intermesh or areinterwoven with each other. Due to the persistence of the fluorescentscreen, the optical effect is the same as though the `picture werecomprised of 77 lines occurring in succession. At the outset, it wasstated that an 80-line picture was to be reproduced. This assumption wasfor convenience.

The frequency channel required for a T7-line picture in my improvedsystem will be that corresponding approximately to a l-line picture.With such a low limit of channel requirement for a 'f7-line picture, itwould be feasible to change to a picture of more lines, up to thelimitation imposed by transmission requirements.

From the foregoing, it will be seen that by my improved method andsystem it is possible to substantially increase the number of picturelines withoutincreasing the required frequency channel. Furthermore, byusing my improved method of scanning, the optical eifect, referred to asflicker, is eliminated or reduced to a negligible degree.

Another advantage of my improved method and system resides in the factthat standard sound film can be run at the normal rate, and thefluorescent screen in the cathode ray tube at the receiving station can,at the same time, be scanned in such manner as to obtain the fulladvantage of the fluorescent effect, all without requiring cumbersomeand costly constructions, as heretofore.

The term apertures or opening is used in the specification and claims ina broad sense, and is intended to cover the various well-knownmodifications such, for example, as the disc construction with lensesinserted in apertures or openings. The term vertical deflection cycle,as used in the claims, means the complete cycle of deflection caused bythe vertical deecting means, this complete cycle consisting of a usefuldeecting period and a return line period.

The terms horizontal deection and vertical deflection, as used in theclaims, refer to the fast and slow deflections, respectively, and arenot limited to the direction of viewing or space location of thedeiiections.

Various modifications, within the conception of those skilled in theart, are contemplated.

I claim as my invention:

1. A system for producingv television images utilizing a skip linescanning which comprises a cathode ray tube having a fluorescent screenand having means to develop a cathode ray and means for causing thedeveloped ray to produce the effect of varying intensities of light andshadow on said uorescent screen, means for producing a deflection of theray in its passage through the tube to cause the ray to traverse thesaid screen in paths bearing an angular relationship to each other, andmeans coordinated with the deilecting means for alternately changing thepredetermined control paths of position at which the ray produces thefluorescent effects to cause successive traversals of the completepredetermined pattern traced upon the fluorescent screen to beinterspersed.

2. A Atelevision receiver comprising the combination of a cathode raytube having a target element and means to develop'a cathode ray andmeans for causing the cathode ray to traverse in a series of adjacentlines a predetermined pattern on the target element, and means forcausing at the completion of each of a plurality of lines of travelcorresponding substantially to an entire image representation, aseparation between successive complete paths of traversal .so as toproduce an interspersed series of complete traversals wherein theindividual lines of each image representation alternate.

3. In the art of television wherein it is required that synchronizingand framing impulses be developed during the succeeding picture periods;the steps in the method of operation which comprise developing duringevery other picture period a framing impulse originating substantiallysimultaneously with a synchronizing impulse, and developing during theremaining intervening picture periods a framing impulse originatingbetween succeeding synchronizing impulses.

4. In a television transmission system for moving picture lm, means forsupporting and imparting feeding movement to a film, means fordeveloping picture signals comprising a rotatable disc for scanning saidfilm, said disc being provided with picture apertures all of which aredisposed on a single circle concentric to the axis of rotation thereof,and means for rotating said disc; said system being characterized by thefact that the rate of feeding movement of the film, 1n terms of picturesper second, is twice the rate of rotation of said disc, in terms ofcomplete revolutions per second, and further characterized in that thenumber of said apertures divided by said rate of feeding equals a wholenumber plus onehalf. v

5. A television receiver comprising a cathode ray tube having thereinmeans to develop a cathode ray and a fluorescent screen-to produceluminous effects, means arranged in cooperative relationship with thecathode ray tube for causing the developed cathode ray to traverse thescreen along a series of substantially parallel paths, and means toproduce at the completion of a predetermined number of parallel paths oftraversal a second series of substantially parallel paths interlacedwith respect to the flrst series of parallel paths so that alternatelyproduced series of complete traversals of the screen by the cathode rayare interspersed.

6. A system for producing television images utilizing skip-line scanningwhich comprises a cathode ray tube having means to develop a cathode rayand means for causing the developed ray to produce the effect of varyingintensities of light and shadow on the fluorescent end wall ofthe tube,means for producing a deection of the ray in its passage through thetube to cause the ray to traverse the screen in paths bearing an angularrelationship to each other, and means coordinated with the deectingmeans for alternately changing the predetermined controlled paths ofposition at which the ray produces the fluorescent effects to causesuccessive traversals of the complete predetermined pattern traced uponthe tube wall-to be interspersed.

Y '7. A television receiver comprising the combination of a cathode raytube having means to develop a cathode ray and means for causing thecathode ray to traverse in a series of adjacent interpersed scanninglines,

10 quency rate of x,

8. In the art of television, the method oiuscan-l ning a picture areawhich comprises deiiecting a scanning ray vertically and simultaneouslycausing the scanning ray to traverse the entire width of said area aplurality of times and a fraction oi' said width once during a verticaldeectingcycle, said fraction being greater than one-eighth, and nextcausing said ray to again traverse the entire width of said area aplurality of times and a fraction of said width once during the nextvertical deflection cycle, said lastmentioned fraction being the same asthe rstmentioned fraction, and interlocking said vertical deection andsaid width traversals to maintain'a xed frequency relation therebetween,said fraction having a numerator and a denominator each of which is awhole number.

9. In the art of television, the method of scanning a picture area whichcomprises causing a scanning ray to traverse said area both horizontallyand vertically to produce during a vertical deflection cycle a pluralityo1' scanning lines each having a certain length and an additionalscanning line having a length which is a fraction of the length of anyone line of said plurality o! lines and next causing said ray to againtraverse said area both horizontally and vertically to produce during avertical deilection cycle a plurality of scanning lines each having acertain length and an additional scanning line having a length which isa fraction of the length o1' any one line of said plurality of lines,and maintaining a xcd frequency relation between said horizontal andvertical traversals, whereby the scanning lines produced by one scanningof said area lie between the scanning lines produced by a precedingscanning of said area to produce a plurality of the repetition of saidscanning being fast enough and said traction being large enough to causeall of said interspersed lines to be visible to an observer due topersistence of vision.

10. In a television system, means for causing a scanning ray to traversea given area horizontally :c times per second, -means for causing saidray simultaneously to traverse said area vertically y times per second,and means for interlocking said tlrst means and said second means tomaintain a fixe frequency relation between a: and y, where y is equal toa whole number plus l/, and where y is at least equal to the rate atwhich persistence of vision substantially causes ilicker disappearancewhereby said scanning ray produces a scanning pattern which appears tobe a fixed stationary pattern of interspersed scanning lines.

11. In a television system, a cathode ray tube, means for deiiecting thecathode ray at a freode ray simultaneously at a frequency rate of y,

deection at the rate1 y,

- pattern of interspersed 4ber greater than 1 which is l the nextvertical means for deflecting the cathamazes means for maintaining a xedfrequency relation between the deflectionv at the rate a: and the wherel is equal toa whole number plus l. and where u is at least equal to therate at which persistence oi' vision substantially causes flickerdisappearance whereby said cathode ray produces a scanning pattern whichappears to be iixed stationary scanning lines.

l2. In a television system, means for producing horizontal synchronizingimpulses occurring at a frequency z, means for producing verticalsynchronizing impulses occurring at a frequency y, and means forinterlocking said rst means and said second means to maintain a xedfrequency relation between :c and 1r, where K whereby said area isscanned successively K times .with the scanning lines oi' saidsuccessive K scannings of said area interspersed or interlaced, A beinga whole number less thanx, and where y is such a value that and where'is a whole numso small that the K number of scannings are repeated at arate at least equal to that at which persistence of vision substantiallycauses icker disappearance.

14. In the art oi' television, the method of scanning a picture areawhich comprises deilecting a scanning ray vertically and simultaneouslycausing the scanning ray to traverse the entire width of said area aplurality of times and a fraction of said width once during a verticaldeection cycle, said fraction vbeing greater than oneeighth, and nextcausing said ray-to again traverse the entire width oi' said area aplurality oi' times and a fraction of said width once during deflectingcycle, said lastmentioned fraction being the same as the firstmentionedfraction, interlocking said vertical deection and said width traversalsto maintain a fixed frequency relation therebetween, and completing thecycle of scanning by repeating the vertical traversal n times per cycleof scanning where .l n is the selective fraction.

' vRANDALL c. Banaan.

